After a while, you will attract a mob of folks following you around which can be a bit scary because you can hardly see out the helmet - especially when you still have the rounded lens instead of the flat ones. I've spoken to some of the 501st members and they mentioned they would occasionally come across the type who would give you a whack behind the helmet. The worse thing I'v experienced so far was some geek grabbing me around the neck when having a photo taken. Always try to have somebody with you who can shout warnings to you like "look out for the guy with a bag of vomit!" or "baby with pocket knife below!" or whatever.
